1. Field of the Invention
The present invention relates to a thermal assisted magnetic recording head with a plasmon generator.
2. Description of the Related Art
Recently, in a magnetic recording apparatus typified by a magnetic disk apparatus, there has been a need for performance improvement of a thin film magnetic head and a magnetic recording medium in association with high recording density. As the thin film magnetic head, a composite type thin film magnetic head is widely used in which a reproducing head having a magnetoresistive effect element (MR element) for reading, and a recording head having an induction-type electromagnetic transducer element for writing, are laminated on a substrate.
The magnetic recording medium is a discontinuous medium in which magnetic grains are aggregated, each magnetic grain has a single magnetic domain structure. Each recording bit on the magnetic recording medium is configured with a plurality of magnetic grains. In order to enhance the recording density, the unevenness of a boundary between recording bits that are adjacent to each other has to be smaller, and the magnetic grains have to be reduced in size for this purpose. However, small magnetic grains, i.e., magnetic grains with small volumes, cause a reduction in thermal stability of magnetization. In order to solve this problem, it is effective to increase anisotropy energy of the magnetic grains. However, high anisotropy energy of magnetic grains enhances a coercive force of the magnetic recording medium, and makes it difficult to record information with an existing magnetic head.
As a method for solving this problem, a so-called thermal assisted magnetic recording is proposed. In this method, a magnetic recording medium with greater coercive force can be used. When information is recorded, a magnetic field and heat are simultaneously added to a portion in the magnetic recording medium where information is recorded, and temperature of the portion is increased. Information is recorded to the portion where the coercive force has been decreased with this process, by the magnetic field. Hereafter, a magnetic head that is used in the thermal assisted magnetic recording is referred to as a thermal assisted magnetic recording head (TAMR head).
A typical TAMR head includes a core that propagates light irradiated from a laser diode and a plasmon generator that generates near-field light (NF light). The plasmon generator is coupled with portion of a propagation light that propagates in the core in a surface plasmon mode and generates a surface plasmon, allows the surface plasmon to propagate up to a front end surface positioned on an air bearing surface, and generates the NF light on the front end surface.
In the existing TAMR head, deterioration of recording properties (such as an S/N ratio) in association with continuous recording occurs. Agglomeration of the front end surface of the plasmon generator is recognized as a main factor. Agglomeration is a phenomenon where metal atoms are gathered, and occurs as a result of dispersion or movement of the metal atoms using heat and stress as a driving force. Asperities exist on the air bearing surface of a magnetic head slider and a surface of the magnetic recording medium, and the front end surface of the plasmon generator may contact the magnetic recording medium while the magnetic recording apparatus is in operation. Temperature increase and stress increase due to the impact that occurs at this time causes agglomeration. The agglomeration easily causes the front end surface of the plasmon generator to recess from the air bearing surface. As a result, the distance between the plasmon generator and the magnetic recording medium is increased, and the capability to heat the magnetic recording medium is decreased over time, which causes deterioration of the S/N ratio. Therefore, it is desired to suppress agglomeration of the plasmon generators to ensure the reliability of the TAMR head.
One option to suppress agglomeration considers improvement of hardness by adding 0.2 at % to 2.0 at % of element, such as copper (Cu) or iron (Fe), to gold (Au), which is suitable for a material of the plasmon generator, for creating an alloy (U.S. Pat. No. 8,964,514). However, an alloy, such as AuCu or AuFe, is poor in a propagation efficiency of the surface plasmon, and propagation loss of the plasmon is great in a plasmon propagation region of the plasmon generator, and causes heat generation. As a result, reliability is reduced. Therefore, even though suppression of the recess of the front end surface of the plasmon generator from the air bearing surface is realized, the problem of heat generation due to a propagation loss of the plasmon occurs.
In the meantime, in U.S. Pat. No. 9,129,620, a technology to form a metal layer, an oxide layer, a nitride layer, a carbide layer or the like as an adhesion layer on a front end surface of a peg of the plasmon generator positioned on the air bearing surface is disclosed. Thus, if the adhesion layer is arranged in the vicinity of the air bearing surface, agglomeration of Au configuring the plasmon generator is suppressed. However, if specifically a metallic adhesion layer is arranged on the air bearing surface, it is not preferable because it prevents collection of light and generation of strong NF light by Au. However, an oxide layer is preferable because loss is small and it has minimal negative effect on the collection of light and generation of strong NF light by Au. However, BeO, SiO, FeO, ZrO, MnO, CdO, MgO and HfO, which are oxide layers disclosed in this publication, have insufficient adhesion with Au, and the suppression of agglomeration is poor.
Non-Patent Literature “Surface Science, Vol. 28, No. 2, pp. 67 to 71, 2007,” discloses a technology in the semiconductor field to provide an adhesion layer, such as Ta or Cr, on an interface between a Cu wiring and a dielectric body (SiOx or SiNx) surrounding the Cu wiring in order to enhance resistance to electromigration of the Cu wiring. However, if the adhesion layer, such as Ta or Cr, is provided in the plasmon generator of the TAMR head, oxygen that transmits a protective film of the head oxidizes Ta or Cr configuring the adhesion layer on the polished air bearing surface, and there is the problem that the adhesiveness will be reduced. Such a problem of adhesion reduction due to oxidation is also disclosed in Non-Patent Literature “Electromigration Reliability Study of Submicron Cu Interconnections,” authored by C-K Hu., R. Rosenberg, W. Klaasen, A. K. Stamper, which begins on page 691″.
The objective of the present invention is to provide a thermal assisted magnetic recording head that can generate a narrowed-down near-field light and that causes minimal agglomeration of the plasmon generators on the front end surface.